Jason Ulseth, executive director of the Chattahoochee Riverkeeper, was on a routine Friday morning patrol when he saw them. Dead fish floating by, one after another. Then he looked at the banks. Thousands of fish — catfish, bass, bream, carp — lined 20 miles of the Chattahoochee River downstream of Peachtree Creek in west Atlanta.
Not a spill. Not sabotage. Just a city's century-old sewer system doing exactly what it was designed to do — and what it should never have been designed to do.
Three Ingredients, One Catastrophe
The fish kill wasn't caused by one thing. It was the collision of three forces that, individually, the river could have survived. Together, they were lethal.
First: the drought. In the weeks before the kill, a prolonged dry spell had reduced the Chattahoochee to just 750 cubic feet per second — the absolute minimum flow that the U.S. Army Corps of Engineers will allow. The river was running on life support. Low water means less dilution capacity, higher temperatures, and less dissolved oxygen. Every fish in that stretch was already stressed.
Second: the storm. During Wednesday rush hour on May 20, a storm dropped three inches of rain in a single hour inside Atlanta's I-285 perimeter. That water hit sun-baked pavement — roads, parking lots, rooftops — and heated up fast. It washed oil, fertilizer, pet waste, tire rubber, and decades of accumulated urban grime off every surface and into the nearest drain. All of it funneled into Peachtree Creek.
Third: the overflow. That torrent of hot, polluted stormwater overwhelmed Atlanta's combined sewer system and the West Area Tunnel — an 8.5-mile underground storage tunnel built to hold raw sewage and stormwater during heavy rains. The tunnel filled completely and overflowed, sending untreated sewage directly into Peachtree Creek and the Chattahoochee River.
The math was simple and brutal: the volume of hot stormwater and raw sewage pouring into the river exceeded the volume of water already in it. Dissolved oxygen crashed to zero. The fish suffocated.
A 19th-Century System in a 21st-Century Storm
Atlanta's sewer system dates to the late 1800s. Like many American cities of that era, large portions were built as combined sewer systems — a single pipe carrying both sewage and stormwater. When skies are clear, the system works. When it rains hard, the combined flow overwhelms the pipes' capacity, and a mixture of raw sewage and stormwater is dumped directly into waterways. These events are called combined sewer overflows, or CSOs.
By the 1990s, Atlanta's CSOs were dumping billions of gallons of diluted raw sewage into the Chattahoochee every year. Sanitary sewer overflows — failures in the separate sewer lines — were occurring hundreds of times per year. Peachtree Creek ran brown after every significant rainstorm.
In 1998, the EPA, Georgia EPD, and the Chattahoochee Riverkeeper filed a federal consent decree forcing Atlanta to fix the problem. The city has spent more than $4 billion since then — building deep storage tunnels, rehabilitating thousands of miles of pipe, upgrading pump stations, and modernizing treatment plants.
The West Area CSO Tunnel, which cost over $400 million alone, was one of the crown jewels of that investment. It was designed to capture overflow during storms and hold it for later treatment. On May 20, the storm filled it to capacity and then some. The system that was supposed to prevent exactly this kind of disaster could not handle what the sky threw at it.
The Investigation
The Georgia Department of Natural Resources, the Georgia Environmental Protection Division, Atlanta's Department of Watershed Management, and the Chattahoochee Riverkeeper are all conducting investigations. Water quality samples were collected over the weekend of May 24-25. Atlanta DWM Commissioner Greg Eyerly met directly with the Riverkeeper on the day of discovery to coordinate the response.
The Riverkeeper's preliminary findings point to four contributing factors:
- Historic stormwater flows from Peachtree Creek carrying thermal pollution and toxic runoff
- Near-record low river flows from the drought, eliminating the river's ability to dilute pollutants
- Combined sewer overflow from the City of Atlanta's West Area Tunnel, discharging untreated sewage into the creek and river
- Treated discharges from surrounding wastewater facilities adding low-oxygen effluent to an already oxygen-depleted system
Ulseth also reported finding black muck — likely raw sewage sediment from the tunnel overflow — along the riverbanks for miles downstream of Peachtree Creek.
This Was Predictable
Nothing about this event was unforeseeable. Combined sewer overflows happen in Atlanta during every major rainstorm. The city has been under federal court order to fix the problem for 28 years. It has spent $4 billion and counting. And still, when a bad storm meets a low river, the system fails catastrophically.
The uncomfortable truth is that Atlanta's combined sewer problem — like similar problems in cities across America — cannot be fully engineered away with tunnels and pipes alone. The fundamental design flaw is the combined part: mixing sewage and stormwater in the same system guarantees that heavy rain events will overwhelm treatment capacity. You can build bigger tunnels. You can add storage. But at some point, the volume of water falling from the sky will exceed whatever capacity you've built.
The real solutions are upstream: green infrastructure that absorbs and slows stormwater before it enters the sewer system. Permeable pavement. Bioswales. Rain gardens. Urban tree canopy. Restored floodplains. These approaches reduce the volume of runoff that reaches the combined system in the first place, reducing the frequency and severity of overflows.
Atlanta has made some investments in green infrastructure, but the overwhelming majority of its consent decree spending has gone to gray infrastructure — tunnels, pipes, and treatment plants. The result is a system that works most of the time but fails exactly when it matters most: during the intense storms that climate change is making more frequent.
The River Remembers
The Chattahoochee River supplies drinking water to much of metro Atlanta. It's the lifeblood of a region of six million people. It is also, historically, one of the most abused urban rivers in the country — decades of sewage overflows, industrial discharge, and suburban runoff have left their mark.
The fish kill of May 2026 is not an isolated event. It is the latest symptom of a chronic disease: a city and a region that grew faster than its infrastructure, deferred maintenance for decades, and is now paying the price — literally, in some of the highest water and sewer rates in the nation, and ecologically, in thousands of dead fish lining 20 miles of river.
The Chattahoochee Riverkeeper, led by Ulseth and a small team of scientists and advocates, has been patrolling this river and holding the city accountable for years. They were the ones who found the fish. They were the ones collecting samples before any government agency arrived. That's what watchdog organizations do — they see what no one else is looking at.
Twenty miles of dead fish is hard to ignore. The question is whether anyone will still be paying attention when the investigation reports come out, the headlines fade, and the next rainstorm hits.